Carbohydrates are now recognized as being of major importance in many cell-cell recognition events, notably the adhesion of bacteria and viruses to mammalian cells in pathogenesis and leukocyte-endothelial cell interaction through selectins in inflammation (Varki (1993) Glycobiology 3: 97-130). Moreover, sialylated glycoconjugates that are found in bacteria (Preston et al. (1996) Crit. Rev. Microbiol. 22:139-180; Reuter et al. (1996) Biol. Chem. Hoppe-Seyler 377:325-342) are thought to mimic oligosaccharides found in mammalian glycolipids to evade the host immune response (Moran et al. (1996) FEMS Immunol. Med. Microbiol. 16:105-115). Molecular mimicry of host structures by the saccharide portion of lipopolysaccharide (LPS) is considered to be a virulence factor of various mucosal pathogens, which use this strategy to evade a host immune response (Moran et al. (1996) FEMS Immunol. Med. Microbiol. 16: 105-115; Moran et al. (1996) J. Endotoxin Res. 3: 521-531).
The oligosaccharide structures involved in these and other processes are potential therapeutic agents, but they are time consuming and expensive to make by traditional chemical means. A very promising route to production of specific oligosaccharide structures is through the use of the enzymes which make them in vivo, the glycosyltransferases. Such enzymes can be used as regio- and stereoselective catalysts for the in vitro synthesis of oligosaccharides (Ichikawa et al. (1992) Anal. Biochem. 202: 215-238). Sialyltransferases are a group of glycosyltransferases that transfer sialic acid from an activated sugar nucleotide to acceptor oligosaccharides found on glycoproteins, glycolipids or polysaccharides. The large number of sialylated oligosaccharide structures has led to the characterization of many different sialyltransferases involved in the synthesis of various structures. Sialyltransferases have been isolated and characterized from mammals and other eukaryotes and from microbes, including C. jeuni, Neisseria, Haemophilus, and E. coli. (Tsuji et al. (1996) Glycobiology 6:v-vii; U.S. Pat. Nos. 6,503,744; 6,699,705; 6,096,529; 6,210,933; and Weisgerber et al. (1991) Glycobiol. 1:357-365).
Large scale enzymatic synthesis of oligosaccharides depends on the availability of sufficient quantities of the required glycosyltransferases. However, production of glycosyltransferases in sufficient quantities for use in preparing oligosaccharide structures has been problematic. The present invention solves this and other problems.